Leaving my understanding here:
Question 1:
LaunchedEffect should be used when you want that some action must be taken when your composable is first launched/relaunched (or when the key parameter has changed). For example, when you want to request some data from your ViewModel or run some sort of animation…
rememberCoroutineScope on the other hand, is specific to store the Coroutine scope allowing the code to launch some suspend function…
imho, the only relation between them is that you can also use a LaunchedEffect to launch a coroutine…
Question 2: As you can see in the docs, rememberCoroutineScope will keep the reference of the coroutine’s scope in a specific point of the composition. Therefore, if a given composable is removed from the recomposition, that coroutine will be cancelled automatically. For instance, you have the following composable calls A -> B -> C. If you remember the coroutine scope in C and it is removed from the composition, the coroutine is automatically cancelled. But if you remember from A, pass the scope through B and C, use this scope in C, and then C is removed, the coroutine will continue running (because it was remembered in A)…